Automated industrial systems, e.g., autonomous robots, have been developed to be more self-sufficient since the emergence of the first manufactured robots over half a century ago. Unlike the earliest robots, contemporary devices require less human assistance; they are capable of independently functioning and completing tasks in various types of unstructured environments. However, bringing robots and humans into spatial proximity leads to the fundamental concern of how to ensure safety for the human. A heavy industrial robot with powerful actuators and unpredictably complex behavior can cause harm, for instance, by stepping on a human's foot or falling on him. Therefore, detecting the presence of moving objects in the vicinity of robots is crucial for ensuring the safety of people working near the robotic system.
One approach is to equip the robot with motion-detection capabilities. Various motion-detecting technologies exist, including passive infrared detectors (PIRs), Doppler microwave sensors, ultrasonic rangefinders, scanned laser rangefinders, vision-based systems, pressure-sensitive mats, and arrays of infrared emitter/detector pairs, which are known as “light curtains.” PIRs are commonly used for intrusion detection systems; they provide high sensitivity to the presence of warm moving objects. However, PIRs have very wide detection angles (typically 90 to 180 degrees) and are incapable of estimating the distance between moving objects and the robots; they thus provide inadequate data on the bearing (velocity) of a detected human. Doppler microwave sensors sense moving objects over a wide field of view; however, they provide neither range (distance) nor bearing (velocity) information. Additionally, multiple Doppler systems can interfere with each other, precluding their deployment as multichannel systems or on multiple robots. Scanned laser rangefinders can provide excellent range and bearing data; they have fields of view up to 180 degrees. However, scanned laser rangefinders are expensive and present a potential vision hazard from the bright laser light source. In addition, scanned laser rangefinders sense objects along a narrow plane; this requires precise adjustments of the laser to ensure detection of, for example, humans of various heights. Further, scanned laser rangefinders do not distinguish moving objects from stationary ones; they thus require significant computational overhead on the part of the robot controller.
Vision-based systems are expensive and require significant amounts of computing power to reliably detect and locate moving objects. Pressure-sensitive mats can provide good data on the location of the objects, but they are susceptible to damage and wear. In addition, pressure-sensitive mats require unobstructed floor areas for operation; this may not be available in industrial factories. Light curtains require the presence of restricted-access “choke points” at which to locate the sensors and thus are difficult to install. Further, light curtains can sense only along a line at the light curtain location and therefore have a limited field of view.
Historically, ultrasonic rangefinders used in the robotics industry were relatively inexpensive and easy to interface. Additionally, ultrasonic rangefinders have relatively narrow fields of view, making them suitable for multi-channel coverage of the detected area. Therefore, several ultrasonic rangefinders can be operated in close proximity without mutual interference by sequencing their pulsed ultrasonic emissions over time. However, ultrasonic rangefinders do not distinguish between stationary and moving objects and they report only the range between the nearest object and the robot. These sensors are thus unable to detect an approaching object, such us a human being, when another object (for example, a chair, or the robot's own arm) is within the detection field of view or closer than the approaching human.
Consequently, there is a need for automated industrial systems that can reliably detect the range and bearing of one or more moving objects, while ignoring stationary objects in the vicinity of e.g., an autonomous robot, thereby protecting humans in the working environment.